Certain beverage preparation machines use capsules containing ingredients to be extracted or to be dissolved and/or ingredients that are stored and dosed automatically in the machine or else are added at the time of preparation of the drink. Some beverage machines possess filling means that include a pump for liquid, usually water, which pumps the liquid from a source of water that is cold or indeed heated through heating means, e.g. a thermoblock or the like.
Especially in the field of tea and coffee preparation, machines have been widely developed in which a capsule containing beverage ingredients is inserted in a brewing device. The brewing device is tightly closed about the capsule, water is injected at the first face of the capsule, the beverage is produced in the closed volume of the capsule and a brewed beverage can be drained from a second face of the capsule and collected into a receptacle such as a cup or glass.
Typically, beverage preparation machines have a body arranged to circulate a fluid to a connection arrangement having a capsule piercer for connecting a removable support or holder of an ingredient capsule and pierce such capsule during the connection. Liquid is circulated via the connection arrangement into the pierced capsule to form the beverage by mixing the liquid with the ingredient in the capsule. Examples of such beverage machines are disclosed in WO2005/016093 and EP 1 868 473. These two references also disclose the use of different removable supports or holder for use with the same machine body for preparing different kind of beverages.
Typically, fluid systems of beverage preparation machines embed a piston pump. These fluid systems are designed and optimized for delivering a fixed flow of liquid into the capsule under a given pressure. The couple flow/pressure is specifically chosen to fit the type of beverages the machine is arranged to prepare. By design, the characteristics and the performances of the piston pump are well-known and adapted only to this restricted domain: for instance, for preparing beverages with a high flow of liquid injected at a low-pressure.
Typically, a fluid system of a conventional low-pressure machine, for example a coffee machine, is arranged to deliver between 350 and 600 ml/min of water under a pressure comprised between 0 and 5 bars. A fluid system of a high-pressure espresso coffee machine is arranged to deliver between 150 and 300 ml/min of water under a pressure comprised between 15 and 25 bars.
FIG. 1 shows schematically on a graph a typical curve 300 representing the flow/pressure domain covered by a piston pump in a beverage machine, X-axis representing the pressure of the liquid, Y-axis the flow of the liquid. It appears clearly that the curve 300 is non-linear and that very limited couples of pressure/flow are actually achievable.
As a consequence, while a piston pump performs reasonably well in traditional mono-system beverage machines, i.e. machines adapted to prepare beverages with similar flow/pressure requirements, it is not adapted to multi-system beverage machines adapted to prepare different beverages with different flow/pressure requirements.